Synthesis and Structures of Vanadium(III) and -(IV) Complexes with a Tripodal Quadridentate Ligand Containing Alcoholic and Pyridyl or Imidazolyl Functionality

Abstract

Complexes of vanadium(III) and vanadium(IV) were synthesized with the tripodal quadridentate ligands, N,N-bis(2-pyridylmethyl)-2-aminoethanol (Hbpmae) and N,N-bis(2-imidazolylmethyl)-2-aminoethanol (Hbimae). The chemical structures and geometries were determined by X-ray crystallography or spectral measurements. Vanadium(III) formed structurally similar, oxo-bridged, dinuclear complexes with both ligands and exhibited intense absorption bands in the visible region. Upon exposure to air, the vanadium(III) complexes oxidized spontaneously, yielding the respective vana-dium(IV) complexes. The geometry of the vanadium(IV)-Hbpmae complex was very similar to that of the monomeric unit in the corresponding vanadium(III) dimer. The alkoxo group in all four complexes coordinated to a metal center in a pro-tonated form. The geometrical arrangements of the vanadium(IV)-Hbpmae and-Hbimae complexes were different with each other. The intense absorption bands in the visible region of the oxo-bridged dinuclear vanadium(III) complexes were assigned based on molecular orbital calculation.